1. Field of Invention
This invention relates to an electromechanical means for analyzing the condition of combustion engine lubrication oil, and more particularly, to a method and apparatus for indicating when the engine oil should be changed.
2. Description of Prior Art
It is well known in the motor vehicle art that engine mechanical wear is dependent on the lubricating ability of the engine crankcase oil and that its lubricating ability degrades as the engine is operated over time. All vehicle manufacturers that offer combustion engines provide guidelines for determining when engine oil should be changed. There are generally two operating conditions, nominal and severe, which require long and short oil change intervals respectively. Those skilled in the art recognize that nominal engine operating conditions are defined as highway driving in moderate climatic conditions. Severe engine operating conditions are defined as stop-and-go driving, extended idling, short trips (under 4 miles) in freezing weather and trailer towing. Vehicle manufacturers have suggested that the oil be changed approximately every 7,500 miles while operating under nominal operating conditions and every 3,000 miles while operating under severe operating conditions.
Those skilled in the art recognize that the interpretation of engine operating conditions by a motor vehicle operator is inaccurate over extended periods and that the required oil change intervals could be as low as 1,000 miles and as high as 10,000 miles. In prior art, this determination was more accurately performed by directly sensing the engine oil temperature and accumulative RPM. In other prior art the capacitance of the oil is measured while the engine is operating. These prior art methods do not properly account for the effects on oil condition due to extreme climatic temperatures, ambient humidity, and normal engine wear. Most of these prior art methods incorporate on-engine apparatus which is generally too complex for installation by the average vehicle owner. Due to high cost and limited proven technology, these on-engine oil change analyzers will be available to a small segment of vehicle owners.
Those skilled in the art of lubrication know that the most reliable means for determining the condition of any oil is to analyze it directly. The quality factors of an oil sample taken from the crankcase would determine whether the oil has degraded beyond continued usage. It is well known in the art of lubrication that the methodology for accurately determining the quality of oil has been standardized. In addition, testing to these standards requires extensive laboratory analysis on large samples of used oil. However, there presently exists no convenient and low cost analyzer capable of estimating the basic quality factors of used motor oil; viscosity and contamination.